Nonwoven fabrics are defined as planar fiber structure prepared by entangling any kind of fibers such as natural fibers, synthetic fibers, glass fibers, metal fibers, etc., into the form of a sheet-like web under the consideration of individual fiber characteristics, and then binding them either mechanically or physically.
In recent years, nonwoven fabrics are widely used in industry and surrounding of life. As the uses, features and functions of nonwoven fabrics begin to be known to the end users, there have been created a variety of uses of the nonwoven fabrics.
Particularly, out of natural fibers, cellulose fibers are an most abundant bio-resource in the earth, and used by mankind for several thousand years as a low-cost and renewable material that can be repeatedly recycled according to the natural system of generation, degradation and consumption. As such cellulose fibers are considered as an energy and food resource, there have been actively made technical developments for making the use of the cellulose components of plants. Moreover, a recent increase in the need for ecofriendly polymer materials has led to flourishing studies on the cellulose as a substitute for all kinds of functional polymer material and a polymer resource used in industry.
The third hydroxyl group of the cellulose molecule is so reactive as to participate in a chemical reaction such as esterification, nitration, or oxidation. Hence, the cellulose fibers can be transformed into a biocompatible material in a wide range of biomedical applications.
In regards to this, knitted products using oxidized cellulose fiber prepared by oxidization of cellulose are excellent in adhesion to the curved organs and tissues and therefore commercially available as anti-adhesion barriers. But, these products have such a large pore size as to be readily permeable to various cells, blood proteins, or the like, consequently with low efficiency as a separation membrane. Also, there are commercially available film-like products using carboxymethyl cellulose (CMC) prepared by carboxymethylation of cellulose. The film-like products, which have no micro pores, are poor in adhesion and too stiff to handle with ease.
To solve these problems, there has been made an attempt to provide a method of preparing nonwoven fabrics from nanofibers using electrospinning. A representative one of the direct cellulose electrospinning methods is the NMMO (4-methylmorpholine N-oxide) spinning method, which had the difficulty in producing nano-sized fibers and, even when producing fibers in nano size, fails to laminate nonwoven fabrics because of the characteristic of the NMMO solution that tends to solidify at temperature below 80° C.
In an attempt to overcome this problem, Korean Patent Laid-Open No. 2008-0075627 discloses a method of preparing cellulose nanofibers that includes electrospinning cellulose acetate and then carrying out deacetylation of the electrospun cellulose acetate with potassium hydroxide and ethanol. But, the cited patent has no mention about nonwoven fabrics that uses oxidized cellulose and thus can be used as a hemostatic dressing or an anti-adhesion barrier with good biodegradability.
Thus, there is a need for preparation of carboxymethyl cellulose nonwoven fabrics consisting of nanofibers that acts as a separation membrane, readily permeable by various cells, blood proteins, or the like, and is applicable to medical materials such as a hemostatic dressing or an anti-adhesion barrier with good biodegradability.
Another method for preparing cellulose nonwoven fabric includes formation of a wet-laid nonwoven fabric by the paper-making process and subsequent carboxymethylation.
FIG. 1 illustrates a process of preparing a wet-laid nonwoven fabric using the paper-making process, where the method includes the step of (1) pulverizing fibers to obtain pulped fibers, (2) when necessary, repeatedly dispersing the pulped fibers with water used as a paper-making solvent, (3) eliminating water and applying the pulped fibers in the form of a sheet on a paper-making wire or screen 31 using a vacuum pump 32, (4) obtaining a wet-laid nonwoven fabric in the form of a sheet using a pressure roll, and (5) winding the wet-laid nonwoven fabric. The wet-laid nonwoven fabric sheet thus obtained is formed by dispersing extremely short fibers, for example, 0.1 to 10 mm long in water in order to secure uniform dispersion of the fibers and thus superior in uniformity to dry-laid nonwoven fabrics. When carboxymethylated, the wet-laid nonwoven fabric has low oxidization efficiency, leading to the difficulty of the process.
In an attempt to apply a wet-laid nonwoven fabric prepared by the paper-making process to medical use purposes, the inventors of the present invention have contrived a method of carboxymethylating cellulose fibers and then preparing a wet-laid nonwoven fabric using the paper-making process, where the carboxymethyl cellulose wet-laid nonwoven fabric thus obtained has good uniformity and offers convenience and easiness in the process using the cellulose fibers commercially available, thereby completing the present invention.